Because of the relatively high energy loss that typically results from the coupling or aligning of a diode laser to an optical fiber, multiple solutions have been proposed over the years to facilitate efficient transfer of electromagnetic energy, such as lightwave signals, from a laser to an optical fiber. The importance of this problem is underscored by the fact that in conventional lasers, for example, a half micron vertical displacement of an optical fiber results in more than half of the light being lost. Additional impetus to improve the coupling or aligning process has been provided recently by the increasing use of optical systems and circuits in various devices that are in great demand in multiple industries.
Among the numerous proposed solutions to the aligning problem, waveguides that use tapered semiconductor structures appear to minimize loss between a diode laser and a fiber optic cable when those waveguides are placed therebetween. One of the better known tapering structures for semiconductor waveguides is the staircase tapering structure that is disclosed in U.S. Pat. No. 4,932,032 issued Jun. 5, 1990 to T. Koch and U. Koren. While the staircase structure offers many advantages, a significant amount of light beam is still lost within the structure and its fabrication process requires a sequence of lithographic and etching procedures for each step in the staircase.
In an attempt to remedy some of the limitations associated with the staircase tapering method, continuous tapering arrangements for waveguide have been recently developed. Shani et al. in an article published in Appl. Phys. Lett., Vol. 55, No. 23, pp. 2389-2391, proposed a system in which, continuous tapering is achieved by placing different layers of glass between the fiber and the semiconductor laser, thereby allowing the layers of glass to act as a lens or an adapter. However, in the Shani et al. system, because the devices are not integrated, two different aligning steps are required, namely, aligning the laser to the glass waveguide, and aligning the glass waveguide to the fiber.
Another continuous tapering device is disclosed by Zengerle et al. in an article published in Electron. Lett., Vol. 27, pp. 1836-1838, 1991. In the Zengerle et al. waveguide device, tapering is achieved by a) continuously tapering down one layer of semiconductor material and b) continuously tapering up another layer of a different semiconductor material. However, one of the problems with the Zengerle et al. waveguide device is that it cannot be integrated with a laser. Furthermore, the same alignment problems experienced with the Shani et al. device will apply to the Zengerle et al. device as well.
Thus, a problem of the prior an is that the stand-alone waveguide devices have significant alignment problems and are not readily adaptable for use inside a laser cavity. Furthermore, for some important applications, beams of light generated by prior art integrated devices are still not narrow enough for optimal coupling to a fiber optic cable.